Method of manufacturing a semiconductor device and a semiconductor device

ABSTRACT

A method of manufacturing a semiconductor device and the device resulted thereof is disclosed. In one aspect, the device has a heterogeneous layer stack of one or more III-V type materials, at least one transmission layer of the layer stack having a roughened or textured surface for enhancement of light transmission. The method includes (a) growing the transmission layer of a III-V type material, (b) providing a mask layer on the transmission layer, the mask layer leaving first portions of the transmission layer exposed, and (c) partially decomposing the first exposed portions of the transmission layer. Suitably redeposition occurs in a single step with decomposition, so as to obtain a textured surface based on crystal facets of a plurality of grown crystals. The resulting device has a light-emitting element. The transmission layer hereof is suitably present at the top side.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/980,225, which claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Patent Application No. 61/293,094, filed Jan. 7, 2010, thedisclosures of which are hereby incorporated by reference in theirentireties.

BACKGROUND OF THE INVENTION Field of the Invention

The disclosure relates to a method of manufacturing a semiconductordevice comprising a GaN-containing heterogeneous layer stack and aroughened surface for light transmission.

The disclosure also relates to a semiconductor device comprising aGaN-containing heterogeneous layer stack on a substrate, the stackcomprising a n-type doped layer and a p-type doped layer, the stackhaving a GaN top layer with first areas having a roughened surfacesuitable for light transmission.

Description of the Related Technology

It is known in the art that the light emission from anelectroluminescent device or from a light emitting semiconductor diode(a LED) is limited by the total internal reflection occurring at theinterface between the semiconductor substrate wherein the device isfabricated and the surrounding medium. Mostly emission of the light toair, with refractive index of unity, is intended. The semiconductortypically has a refractive index n_(s) of 2 to 4. For instance, therefractive index of GaN and AlN are 2.46 and 2 respectively. Snell's lawdetermines that only photons arriving at the semiconductor-air interfacewith an angle smaller than a critical angle θc=arcsin (1/ns) can espaceto the air. All other photons are totally reflected at thesemiconductor-air interface, and therefore remain in the semiconductorsubstrate, until eventually they are re-absorbed. Typically, thecritical angle for total internal reflection is in the range of 10-20°C. Hence, total internal reflection limits the number of photonsescaping the semiconductor substrate to those photons arriving at thesemiconductor-air interface with an angle below the critical angle. Onlya few percent of the photons generated inside the semiconductorsubstrate comply with this condition. In order to extract more lightfrom LEDs, efforts have been ongoing for several decades that includedwet-chemical etching of a LED surface, employing periodic photoniccrystals, planar graded refractive index antireflection coatings,patterning of substrates, particularly of sapphire substrates, andshaping of LED chips.

EP0977280 discloses the provision of a roughened surface to improve suchlight transmission, in particular, light emission, from a semiconductordevice such as a LED. A roughened surface provides other angles makingthat light emitting in an angle relatively perpendicular to thesubstrate plane still can leave the substrate. Moreover, these angleslead to reflection and recombination with an improved chance ofsubsequent emission. This leads to overall quantum efficiencies in theorder of 20 to 30%. The surface roughening is therein achieved byapplication of a substantially random distribution of particles on thesurface, by reducing the size of the particles and thereafter etchingthe surface while using the particles as a mask. Preferably, use is madeof a monolayer of closed packed colloidal particles. The diameter isreduced by application of an oxygen plasma. The size of the colloidalparticles is not strongly critical, but preferentially they have adiameter λ_(s) that is 50% to 200% of the wavelength of the light in thesemiconductor (λ_(s)=λ₀/n_(s), with λ₀ the wavelength in vacuum andn_(s) the refractive index of the semiconductor). An alternative is theuse of a mask provided by a photoresist. This is particularly relevantfor red, near-infrared and infrared LEDs, since for these wavelengthsthe required texturing features are of the order of 200 nm or larger.This resolution can be achieved by UV or deep UV illumination of asuitable photoresist. EP0977280 discusses specifically GaAs-type layers.However fabrication of submicron patterns by lithography and plasma dryetching is costly, and the etching process could damage the surface ofGaN.

Wet-chemical texturing of an N-face GaN (000-1) surface ofvertical-structured LEDs is disclosed in WO2005/064666. The N-face isthe bottom GaN layer when seen in the order of processing. This etchingoccurs after transfer of the LED to another carrier and removal of theprocessing substrate, typically sapphire. The p-type doped GaN layerthat is the top layer when seen in the order of processing, is howevertoo thin for carrying out the texturing. Wet-chemical etching is knownto be very efficient in enhancing light extraction, and hence, is widelyused in high-power commercial LEDs. However, KOH-based wet-chemicaletching needs additional process steps such as deposition and removal ofa protection layer covering ohmic contact to the n-type GaN. Inaddition, due to crystal-plane-dependent etching rates, it is verydifficult to form non-random, optimized or designed features.

One alternative method is disclosed in U.S. Pat. No. 7,071,494. Use ismade herein of specific growth properties of AlN and AlGaN with anAl-content of at least 50%. Growth herein may occur initially in theform of well textured regions (e.g. crystalline islands) instead of arather randomly oriented matrix, such as explained in M. Auger et al,Surface and Coatings Technology 180-181 (2004), 140-144. Thereafter, thematerial is annealed such that the material becomes crystalline.Subsequently, portions of the annealed layer that surround large stablegrains are optionally etched away with H₂, N₂, NH₃, HCl and mixturesthereof to form a textured layer. In embodiments where the growth favorsthree dimensional growth (i.e. crystalline islands), annealing may besufficient to form the textured layer. A planarizing layer is depositedon top of the textured layer.

The result of this known method is a textured surface of large crystalgrains of AlN or Al-rich AlGaN, which is overgrown by a planarizinglayer of GaN. We observe that the planarizing layer herein effectivelyreduces the refractive effect of the textured surface, as the differenceof the refractive indices of AlN and GaN is less than that between AlNand air or an organic material. Apparently, the insight of U.S. Pat. No.7,071,494 is that the combination of a textured surface with aplanarizing layer provides a suitable surface roughness.

It is however a disadvantage of this known method that the combinationof a textured surface of AlN or Al-rich AlGaN and a planarizing surfaceis a very complex and thus expensive structure for obtaining a roughenedsurface. Moreover, this method of creating a roughened surface shareswith the wet-etching the disadvantage that it is very difficult to formnon-random, optimized or designed features. As admitted in U.S. Pat. No.7,071,494, the large, stable grains will survive the etching process,whereas other portions are etched away.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

A first inventive aspect relates to a method of manufacturing asemiconductor device comprising a heterogeneous layer stack of one ormore III-V type materials, at least one transmission layer of the layerstack having a roughened surface for enhancement of light transmission.The method comprises 1) growing the transmission layer of a III-V typematerial, 2) providing a mask layer on the transmission layer, the masklayer leaving first portions of the transmission layer exposed, and 3)partially decomposing the first exposed portions of the transmissionlayer, therewith obtaining the roughened surface.

The inventor has been found to his surprise that the decomposition stepresults in the formation of an adequate roughened surface, but only if amask layer is present on the transmission layer, first portions of thetransmission layer being exposed.

In a most preferred embodiment, redeposition of the III-V material iscarried out generating crystal facets defining a textured surface. Theformed crystal facets overcome a major disadvantage of the prior art:the size is relatively uniform. Moreover, the method can be tuned so asto vary density and size of the crystal facets. Furthermore, thetransmission layer with crystal facets is stable.

The redeposition suitably occurs in a single step with the decompositionof the transmission layer. This is particularly achieved by tuning thecomposition of the atmosphere in which the single step decomposition andredeposition is carried out. Particularly, this is a nitrogen-richatmosphere. Atoms liberated by the decomposition are then redeposited,but at another location on the surface that is more energeticallyfavorable.

Suitable materials for the transmission layer are materials that have arelatively low decomposition temperature, particularly lower than about1250° C. Use of such materials for the transmission layer enabled tocarry out the step in a controlled manner. Moreover, damage to otherlayers within the heterogeneous layer stack is kept at a low level.Preferably, the step is carried out at a lower temperature than about1250° C., for instance in a range of about 800-1150° C. Suitablematerials include GaN, InN, InGaN and Al-poor alloys of these materials,such as Al_(x)Ga_(1-x)N, with x≤0.3. In the suitable embodiment that thetransmission layer forms also the p-type doped layer of the lightemitting diode, the decomposition step may be combined with one of theanneal steps typically carried out on the p-type doped layer. This ishowever not necessary

In a most suitable embodiment, the transmission layer is present on astop layer. The stop layer remains intact when decomposing thetransmission layer. The use of such a stop layer is a gentle manner ofdefining an end point to the decomposition treatment. As such, it canfurther be exploited to define the size of the crystals. Suitably, thestop layer comprises a material different from the transmission layer.One advantageous implementation hereof is that the material of the stoplayer has a decomposition temperature higher than that of thetransmission layer. A most suitable combination is that of atransmission layer of GaN and a stop layer of AlGaN.

According to a second aspect of the disclosure, a semiconductor deviceis provided that comprises a heterogeneous layer stack of one or moreIII-V type materials. At least one transmission layer of the layer stackhas a roughened surface for enhancement of light transmission obtainableby the method.

According to a third aspect of the disclosure, a semiconductor device isprovided that comprises a heterogeneous layer stack of one or more III-Vtype materials. At least one transmission layer of the layer stack has aroughened or textured surface for enhancement of light transmission.Herein the surface is a textured surface defined by crystal facets of aplurality of crystals grown in first exposed portions of thetransmission layer, the plurality being in a range of about0.01-1000·10⁶/mm².

In one aspect, the transmission layer is provided with a texturedsurface in the form of a plurality of crystals having crystal facets.The plurality is particularly a large number, e.g. about0.01-1000·10⁶/mm², preferably about 0.1-100·10⁶/mm², particularly about1-50·10⁶/mm². Suitably, the diameter of a single crystal is in the rangeof about 50 to 800 nm. Therewith, the surface is textured in ahomogeneous manner, e.g. the crystals are sufficiently fine, andnevertheless with sufficiently large crystal facets to increase thetransmission of radiation. The crystals are grown here, as a consequenceof the redeposition step. This in-situ and actual growth results inbetter and more uniform shapes than obtained when the textured surfaceare created by etching.

In one particular embodiment, the textured surface is made to beoptically transparent for a selected range of wavelengths. This selectedrange of wavelengths suitably corresponds to the wavelength of theradiation emitted by the semiconductor device, i.e. any light emittingdiode or transistor therein. The transparency for other wavelengths isthen typically less than the transparency for the selected range. Therange of wavelengths may be defined by tuning the formation of thecrystals, and particularly thereof the depth to which the transmissionlayer is decomposed for the formation of the textured surface.Optionally, the transmission layer is present on a stop layer thatdefines the depth to which the transmission layer is decomposed. Thewavelength may be further tuned by setting the atmosphere in whichdecomposition occurs (more specifically the nitrogen-content of theatmosphere defining the speed of redeposition). Additionally, thematerial of the transmission layer can be varied.

The textured surface is obtained particularly by decomposition through amask. In one advantageous embodiment, at least a portion of the areadefined by the mask is subsequently used for the provision of a contact.The mask may herein be removed completely and then replaced by a metalcontact. Alternatively, holes may be defined through the mask. The maskareas are very suitably for subsequent layer deposition due to theplanarity of their surface.

As is hereinabove specified with reference to the method, thetransmission layer suitably comprises a material with a relatively lowdecomposition temperature, particularly lower than about 1250° C. Use ofsuch materials for the transmission layer enabled to carry out the stepin a controlled manner. Moreover, damage to other layers within theheterogeneous layer stack is kept at a low level. Preferably, the stepis carried out at a lower temperature than about 1250° C., for instancein a range of about 800-1150° C. Suitable materials include GaN, InN,InGaN and Al-poor alloys of these materials, such as Al_(x)Ga_(1-x)N,with x≤0.3.

The device suitably comprises further at least one light emittingelement, such as a light emitting diode. Preferably, the light emittingdiode is a blue light emitting diode (LED). It has been found that thesize of the crystals matches best with blue light, which can begenerated most advantageously in GaN-based LEDs. The term blue LED isherein to be understood to refer to a LED able of emitting of blue,violet and/or ultraviolet light, i.e. with a wavelength suitable in therange between about 300 and 500 nm, particularly between about 400 and500 nm and especially between about 450 and 500 nm.

Alternatively, the device may be a solar cell or a hydrogen generator.The latter device is particularly a device based on a InGaN layer thatis in operation present within a reservoir of water or an aqueoussolution. A junction is then formed between the InGaN and the water.This junction may split water into hydrogen and oxygen, upon provisionof a suitable voltage to the InGaN.

Suitably, the textured surface is present at a top side of the devicewhen seen in the order of processing. Typically, this top side is theside at which the p-type GaN is present. This evidently has theadvantage that it takes away the need of removing the processingsubstrate. In one implementation the textured surface is covered with asilicon nitride protection layer. Such a silicon nitride layer forms anadequate passivation, and it is optically transparent and has anadequate reflection coefficient. A most suitable version thereof is anin-situ silicon nitride layer, which is a silicon nitride layer that isdeposited with chemical vapor deposition, subsequent to otherprocessing. Particularly, it is deposited without an intermediatecooling step to room temperature.

In a further implementation, the presence of the textured surface on thetop side is combined with the presence of an optical element on thebottom side of the device (e.g. the side of the processing substrate).Such optical element is more particularly a grating or a mirror. Thiselement is intended for reflecting and/or otherwise guiding thegenerated light. As a result, the light may be directed to the top side,where it adds to the overall efficiency. Moreover, such reflection orguiding suitably changes the orientation of the light. It then may havea higher chance to escape from the element into the air.

According to a fourth aspect of the disclosure, an electronic device forconfinement of radiation is provided. The radiation is confined into ananostructure, located within a substrate of the electronic device, bymeans of surface plasmonic structures on a surface of the substrate.Herein, the surface is a textured surface defined by crystal facets of aplurality of crystals of a transmission layer of a III-V material.

It has turned out that a textured surface defined by crystal facets ishighly suitable for use as a surface plasmonic structure. In a mostsuitable implementation, it is thereto covered, at least partially, withan electrically conductive layer, such as a metal, or a conductivenitride or both. The conductive layer is deposited conformally so as notto loose the textured structure. The nanostructure is for instance acavity or a pore. The textured surface is most suitably prepared by themethod. Alternative methods are however not excluded. The nanostructureis suitably defined in an area covered by a mask during the formation ofthe textured surface. This device is suitably used for the detection ofproperties of individual molecules, and more particularly biomoleculessuch as DNA molecules, proteins and the like. Thereto, suitablyradiation transmitted through the nanostructure is detected. Theprinciple hereof is described in the non-prepublished applicationPCT/EP2009/066737 in Applicant's name, which is herein incorporated byreference.

In one important embodiment, a light emitting element is present foremission of radiation that is directed to the nanostructure through thesurface plasmonic structures. A separate laser is conventionally used asa light source in optical detection. The combination of a light emittingelement and the textured surface acting as a surface plasmonic structuremay replace the separate laser. This replacement simplifies the set upof such optical detection apparatus and moreover reduces costconsiderably.

In a further implementation, the electronic device is used in anapparatus further comprising means for translocating molecules throughthe nanostructure and a detection unit for detecting electromagneticradiation at least partially generated by excitation of surface plasmonpolaritons in the nanostructure and exiting from the nanostructure. Theapparatus additionally comprises a light source that is either the lightemitting element in the device or an external light source, or acombination of both.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a-d is a series of diagrammatical, cross-sectional views of stagesin the method according to a first embodiment

FIG. 2 is a diagrammatical, cross-sectional view of the result of themethod according to a second embodiment

FIG. 3a-b show diagrammatical, illustrative view of prior artdecomposition;

FIG. 4a-b show diagrammatical, illustrative views of one embodiment ofthe method, and

FIG. 5 is an image made by scanning electron microscopy (SEM) of thetextured surface in accordance with one embodiment.

DETAILED DESCRIPTION OF CERTAIN ILLUSTRATIVE EMBODIMENTS

The present disclosure will be described with respect to particularembodiments and with reference to certain drawings but the disclosure isnot limited thereto but only by the claims. The drawings described areonly schematic and are non-limiting. In the drawings, the size of someof the elements may be exaggerated and not drawn on scale forillustrative purposes. The dimensions and the relative dimensions do notcorrespond to actual reductions to practice of the disclosure. Equalreference numerals in different figures refer to same or like elements.

Moreover, the terms top, bottom, over, under and the like in thedescription and the claims are used for descriptive purposes and notnecessarily for describing relative positions. It is to be understoodthat the terms so used are interchangeable under appropriatecircumstances and that the embodiments of the disclosure describedherein are capable of operation in other orientations than described orillustrated herein.

FIG. 1a-d is a series of diagrammatical, cross-sectional views of stagesin the method according to a first embodiment. The method starts withthe configuration of FIG. 1a comprising a substrate 1 and a transmissionlayer 2 of a III-V material. The substrate 1 typically comprises a stackof layers of a III-V material which defines a light emitting element.The combination of such layer stack in the substrate 1 with thetransmission layer 2 constitutes the heterogeneous layer stack of III-Vmaterial as recited in the claims.

A suitable configuration of the stack of layers is a quantum wellstructure interposed between a first device layer that is n-type doped,and a second device layer that is p-type doped. Manufacturing relatedreasons make that the n-doped layer is usually the bottom layer and thep-doped layer is the top layer. The quantum well structure suitablycomprises a stack of alternatingly a first layer and a second layer.Most suitably, the quantum well structure comprises first layers of GaNand second layers of InGaN. The first and the second device layer aretypically GaN layers. Suitably, the transmission layer 2 is present ontop of the active layer stack, e.g. the quantum well structure and thefirst and second device layers. It is however not excluded, that thetransmission layer is the first or the second device layer.

The stack is preferably grown on a silicon substrate, which allowsprocessing in semiconductor fab environments. Good results have beenobtained with a silicon (111) substrate, suitably on top of a handlingwafer and a buried insulating layer, such a structure also known as anSOI-wafer with a Si(111) device layer. The GaN layers are grown on the(111) silicon, for which a nucleation layer and thereafter a bufferlayer are deposited. In order to match the lattice constant of Si(111)as good as possible, it is deemed beneficial that the buffer layercomprises Al_(x)Ga_(1-x)N, wherein x is equal or smaller to 1. Suitably,the Al-content decreases with the distance to a top surface of theSi(111) substrate, either gradually or in steps. However, the Si(111) isby no means the only useful substrate material, alternatives includingfor instance Si(001) and sapphire. Moreover, Al_(x)Ga_(1-x)N, wherein xis equal or smaller to 1, is certainly not the only possible bufferlayer. The skilled person in the art of GaN epitaxy will be able to findalternatives in the literature.

Furthermore, while the p-doped GaN layer may be the top layer in thesequence of grown layers, it is not excluded that the transmission layeris provided on the n-type doped GaN. This is then suitably carried out,after that the top layer is attached to another carrier and thesubstrate used for processing has been removed at least partially. As asilicon substrate may be removed easily by wet or dry chemical etching,this is a further reason to use a silicon substrate (or SOI) as theprocessing substrate. The transmission layer 2 may in this case be growneither before the growth of the other layers in the structure or afterremoval of the processing substrate.

It is observed for reasons of clarity that a light emitting diode, in animplementation with a quantum well structure, has been taken as lightemitting element in the present description. Another light emittingelement, such as a light emitting transistor, and another implementationof a light emitting diode, could be applied as an alternative. Moreover,the III-V material of the layer stack in the above mentioned examplecomprises GaN and InGaN as functional layers. This is merely an exampleand other III-V materials and/or a different stack of such materials maybe used. Typical examples include AlGaN, InAlGaN.

FIG. 1b shows a second stage in the manufacturing of the device. Hereina mask 4 has been applied on a surface of the transmission layer 2. Themask suitably comprises a dielectric material. Good results have beenobtained with SiO₂. It is preferably a material onto which no growth ofGaN or like materials occurs. The mask layer is provided with a patternso as to create windows between mask portions. The window definingexposed portions of the transmission layer may have a rectangular, oval,circular or other shape, such as a T-shape. The width of the windows issuitably smaller than about 50 microns and typically larger than about0.5 microns. Good results have been obtained in first experiments withwidths varying from approximately 3 to 20 microns.

The transmission layer suitably comprises a material with a relativelylow decomposition temperature, particularly lower than about 1250° C. atatmospheric pressure. Use of such materials for the transmission layerenabled to carry out the decomposition step in a controlled manner.Moreover, damage to other layers within the heterogeneous layer stack iskept at a low level. Suitable materials include GaN, InN, InGaN andAl-poor alloys of these materials, such as Al_(x)Ga_(1-x)N, with x≤0.3.Layers of AlN and Al-rich AlGaN, for instance Al_(x)Ga_(1-x)N, withx≥0.5, have a higher decomposition temperature than about 1250° C. atatmospheric pressure.

FIG. 1c shows a third stage in the manufacturing of the device. Herein,decomposition and suitably also redeposition takes place. Preferably,the step is carried out at a lower temperature than about 1250° C., forinstance in a range of about 800-1150° C. Particularly good results havebeen obtained in the range from about 1000 to 1150° C. It is typicallycarried out in a Chemical Vapor Deposition reactor, such as typically inuse for the growth of III-V materials. The redeposition rate isinfluenced by setting the nitrogen content in the atmosphere. Thenitrogen-content herein particularly refers to nitrogen available forreacting with decomposed Ga into GaN. One suitable manner involves theuse of ammonia (NH₃). Very good results have been obtained withcombinations of ammonia and hydrogen (H₂). Mixtures of oxygen andnitrogen could be used alternatively. Preliminary experiments showedthat a threshold of the nitrogen content exists: only decomposition(i.e. no redeposition) is found to take place below a threshold level.The actual threshold appears dependent on typical process conditionssuch as the temperature of operation, the material of the transmissionlayer, and other gases present in the atmosphere. The equipment in usemay further play a role.

A plurality of crystals 3 with crystal facets 31 defining the texturedsurface are thus formed. The crystal facets 31 for instance have a(10-10) or (1-101) orientation in case that the transmission layercomprises GaN. The overall shape of the crystals typically is pyramidal.GaN has a hexagonal structure so that the crystals have a ground planewith a hexagonal shape. Each of the crystal facets then has a triangularshape. It is observed that the actual shape could be different ormodified, or at least less perfect. In comparison to a textured surfacecreated by wet-chemical etching it was found that the present structureis more regular. The variation in size, particularly height is reduced,for instance to a standard deviation of less than about 100 nm,preferably less than about 50 nm. The density of crystals is typicallyreduced, due to the redeposition process in which adsorption occurs atlocations with minimum energy, e.g. in an appropriate crystal lattice.

FIG. 5 is an image made by scanning electron microscopy (SEM) from atextured surface made in accordance with one embodiment. The blackstripes are the masks, in between of which a crystals with crystalfacets are present. A scale indicator is included, demonstrating adistance between neighboring masks of approximately about 7 microns inthis example. Further measurements on the shown example show that anindividual crystal facet had a width of about 353 nm and a height ofabout 385 nm. Several experiments were carried out with temperatures of1000 and 1100° C., growth durations of 1 and 10 minutes in an atmosphereof 8 slm NH₃ and 7 slm H₂. All resulted in the growth of crystals.However, when reducing the NH₃ concentration to 2 about slm, merely someroughening was observed.

The option of decomposition without redeposition may further beexploited to optimize the shape of the crystals formed in the step. Forinstance, the generation of the textured surface may be finalized with astep below the threshold level. The decomposition occurring then maygive rise to modifications of the overall shape of the textured surfaceand/or to the size of crystal facets.

FIG. 1d shows the result of a further optional stage. In this furtheroptional stage the decomposition is continued, resulting in a smalleramount of crystals having crystal facets of larger size and having alarger diameter. Since the diameter of the crystals is in the range ofthe wavelength light (about 300-800 nm), an increase in the diameter ofthe crystals makes the textured surface more suitable for lighttransmission of light of larger wavelength (for instance from blue toorange).

FIG. 2 shows the result of the manufacturing according to a furtherembodiment. Herein, a stop layer 5 is present. The stop layer 5 issuitably present on other layers 6 on top of a substrate 1. The stoplayer 5 preferably has a decomposition temperature higher than thetransmission layer 2. When GaN is chosen as the material of thetransmission layer 2, AlN or Al-rich AlGaN is a good choice for the stoplayer 5. When InGaN is chosen as the material of the transmission layer2, AlN, AlGaN, but also GaN may be chosen as the material of the stoplayer 5. The stop layer 5 is effective so as to stop the decompositionand redeposition step at a predefined stage of processing. As in theprevious embodiment, the transmission layer 2 may be suitably doped toconstitute a p-type doped layer that is part of a light emitting layerstack further comprising an n-type doped layer and a quantum wellstructure. A suitable dopant is for instance Mg. The stop layer 5 isthen suitably inserted between p-type doped layer or layers 6 and thetransmission layer 2. It is not excluded that both the layer 6 and thetransmission layer are p-type doped. Additionally, the stop layer 5 maybe p-type doped as well. However, the dopant concentration may vary.

The semiconductor device with the textured surface may subsequently beprovided with at least one electrode and suitably a protection layer.One suitable implementation for the electrode is the definition in oneor more of the areas covered by the mask layer 4. The mask layer 4 couldbe replaced by one or more metal contact. Stripe-shaped metal contactsare adequate for providing sufficient surface area without hamperingtransmission of light too much. A suitable metal is for instance a metalthat may be applied as underbump metallization (UBM) for subsequentassembly. Typical material include for instance Nickel (Ni), Tin (Sn),Lead (Pb) and alloys of such metals. Instead of replacing the mask layerafter the texturing by a metal contact, the mask layer could comprisethe metal, or alloy. If desired, the transmission layer 2 may be locallyremoved, for instance by laser or electron beam irradiation, butalternatively by covering the textured surface with another mask such asa photoresist. Alternatively, dopants may be implanted at the area ofthe contact. Another suitable implantation involves the provision of anoptically transparent, electrically conductive layer on top of thetextured surface. A suitable material is for instance indium tin oxide,but tin oxide and electrically conductive polymers may be appliedinstead.

Suitable protection layers include first of all a passivation layer, andadditionally a molding compound. Materials for these protection layersare well known in the art and include silicon nitride, polyimide, epoxy.

FIGS. 3a and 3b, 4a and 4b are diagrammatical figures explainingmolecular mechanisms behind one embodiment. FIGS. 3a and 3b show hereinthe decomposition without application of a mask. FIGS. 4a and 4b showthe decomposition and redeposition that occurs when if mask is present.

Typically, decomposition of GaN involves sublimation of solid-phase GaNinto gaseous GaN (shown as dots 20 in FIG. 3a ). When hydrogen ispresent in the atmosphere, the sublimation may lead to a reaction withGa, GaH, N₂ and NH₃ as reaction products. A careful analysis has beenpublished by M. A. Mastro et al., Phys. Stat. Sol (a), 188 (2001),467-471, which is incorporated herein by reference. As specified in thearticle, annealing in H₂ at 900° C. resulted in the complete sublimationof the GaN film. FIG. 3b shows the result wherein a portion 2 a of thetransmission layer 2 of GaN has been decomposed by sublimation. It isobserved in the article that annealing in an NH₃ atmosphere leads to GaNfilms that are relatively stable.

FIGS. 4a and 4b show the surprising effect of application of a mask.Now, the mask generates a different process, wherein the annealing,particularly in an atmosphere comprising both hydrogen and ammonia,results in decomposition and redeposition. Herein, sublimation of solidphase GaN into gaseous components 20 still occurs. The available ammoniaappears to shift the balance of the sublimation reaction back tosolid-phase GaN. However, the GaN (indicated with dots 21) is nowincorporated into the lattice of the layer on other positions. In thismanner, the more energetically favorable crystal facets 31 are created.Reference is made here to GaN as if it were a molecule that makes atransition from gas phase back into the solid phase. This is notnecessarily a physically correct description of the crystallizationprocess. Ga could be a gas phase single atom that only binds withnitrogen upon integration into the crystal lattice.

In one suitable embodiment, the transmission layer with the texturedsurface is used as a surface plasmonic structure, particularly in amethod of detection of individual molecules and/or their properties.Thereto, a nanostructure is present in which radiation is confined. Thenanostructure is suitably provided with tilted sidewalls. Thenanostructure with tilted sidewalls may be or comprise a nanopore with avarying diameter across the membrane, and, in cross-sectional view, asubstantially triangular shape. The textured surface is most suitablycovered with an electrically conductive layer, for instance a metal suchas a noble metal. One therefore may suitably express the method in theembodiment of detection of transmitted radiation as a method comprisingthe steps of:

directing electromagnetic radiation onto the nanostructure in thedirection of the first major surface, using thereto the textured layeras a surface plasmonic structure,

translocating molecules through the nanostructure, and

detecting electromagnetic radiation that exists from the nanostructureaway from the second major surface, transmission of electromagneticradiation through the nanostructure being at least by excitation ofsurface plasmon polaritons in the nanostructure.

The method is particularly suitable for detection of individualmolecules. Thereto, the nanostructure is suitably configured to limitthe passage of a sample material through the nanostructure to a singlemolecule at a time. The molecule is for instance a double strandednucleic acid molecule or a single stranded nucleic acid molecule or apolypeptide molecule or a single ribosome or a cell or a viral particle.The molecule is translocated through the nanostructure by means of anysuitable driving force, e.g. by electrophoresis. Radiation originatingfrom at least one light source, such as a laser or a led or anotherlight source. The light interacts with the molecule inside the nanopore6, this interaction is the basis for biomolecular analysis. Hence thenanopore can be an optical confinement. Suitably, electromagneticradiation such as light that has been transmitted through the nanopore(rather than only reflected light) is used for the measurements. Thedetection of the radiation occurs by molecular spectroscopy, and morespecifically by Raman spectroscopy, molecular fluorescence spectroscopyor surface enhance infrared absorption spectroscopy. Certain embodimentscan involve the use of nanoparticles to enhance the Raman signalobtained from nucleotides. The nanoparticles may be silver or goldnanoparticles, although any nanoparticles capable of providing a surfaceenhanced Raman spectroscopy (SERS), surface enhanced resonance Ramanspectroscopy (SERRS) and/or coherent anti-Stokes Raman spectroscopy(CARS) signal may be used, e.g. Ag, Au, Cu, Al, Ni, Pt, Pd, particularlynoble metals.

The textured surface is a surface plasmonic structure that can influencethe behavior of optically active molecules in several ways. Firstly, dueto the focusing of electromagnetic radiation to nanovolumes, moleculescan be excited more efficiently. Secondly, the plasmon resonanceperturbs the local electromagnetic mode density, modifying the decayrate of local dipole emitters. Such nano-antennas are particularlysuitable in case that Raman spectroscopy, molecular fluorescence orsurface enhanced infrared absorption spectroscopy is used.

In the case, e.g., of Raman spectroscopy, this double effect leads tothe well known E4 dependence of the Raman scattering intensity on thelocal electric field. It further enables probing of vibrationaltransitions using optical excitation. Additional enhancement can beachieved using resonance Raman (illuminating in resonance with anelectronic transition of the target molecule) or coherent anti-stokesRaman scattering (CARS) (a non-linear, 4-wave mixing process). Ramanspectroscopy is particularly suitable for sensing segments of largermolecules, such DNA molecules.

Preferably, the nanostructure with tilted sidewalls is created such asto create an electromagnetic hotspot. The hotspot is the location wherethe optical interaction is strongest and where structural or chemicalinformation is harvested. It provides a smaller sensing region than whatcan be achieved with traditional lens structures or photonic components.The field confining structure provides plasmonic field confinementleading to localization based on gap mode resonance, at the hotspot. Asa result, the electromagnetic field gets concentrated in the hotspot.Therewith, the hotspot effectively amplifies the optical signal. Theelectromagnetic field results from the interaction of theelectromagnetic radiation with the matter present. Means for enhancementof the field strength, and thus means for creation of the hotspot,include plasmon carrying metal structures, in particular nano-antennas,and a nanostructure in which cavity effects occur, particularly with avarying diameter. In the latter case, the nanostructure is preferablydesigned such that the hotspot is present at the position at whichthe—inner-diameter is smallest. However, alternative shapes of thenanostructure leading to resonance in a limited volume thereof are notexcluded.

In one embodiment, the textured surface as obtainable with the method isused, wherein the pattern of the mask is defined so as to guide thelight towards the nanostructure. For instance, the textured surface hasa stripe-shaped surface area with at one end the nanostructure. In afurther implementation, all elements (e.g. the light emitting element,the textured layer, the nanostructure and the detection method) aretuned to a single operation wavelength. In a further implementation, thenanostructure may be obtained by selective growth of a GaN layer, as isfurther elaborated in patent application PCT/EP2009/066739, which isincorporated herein by reference.

In a further embodiment, the light source is not an external lightsource, but is present within the substrate. Light emitted from thelight source, typically a light emitting diode, is then transmitted viathe textured surface to the nanostructure. While transmissionspectroscopy—and hence a nanostructure extending through thesubstrate—is favorably is used, another form of optical detection is notexcluded. While the textured surface may be used as a plasmonicstructure to provide a desired orientation to the light, it is notexcluded that an additional optical element such as a mirror is used inaddition to the textured surface.

Though the textured surface obtainable with the method appears mostsuitable for use as part of a surface plasmonic structure, it is notexcluded that a prior art textured surface is used that is obtained withf.i. wet chemical etching with KOH.

The foregoing description details certain embodiments of the invention.It will be appreciated, however, that no matter how detailed theforegoing appears in text, the invention may be practiced in many ways.It should be noted that the use of particular terminology whendescribing certain features or aspects of the invention should not betaken to imply that the terminology is being re-defined herein to berestricted to including any specific characteristics of the features oraspects of the invention with which that terminology is associated.

While the above detailed description has shown, described, and pointedout novel features of the invention as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the technology without departing from the spirit ofthe invention. The scope of the invention is indicated by the appendedclaims rather than by the foregoing description. All changes which comewithin the meaning and range of equivalency of the claims are to beembraced within their scope.

What is claimed is:
 1. A method of fabricating a light-emittingsemiconductor device, the method comprising: providing a light-emittinglayer stack; forming a stop layer over the light-emitting layer stack;forming a light-transmission layer on the stop layer, thelight-transmission layer formed of a crystalline III-V semiconductormaterial that is optically transmissive to emission wavelengths of thelight-emitting layer stack; patterning a mask layer on thelight-transmission layer such that portions of the light-transmissionlayer are exposed; thermally texturing in an atmosphere comprisingmolecular hydrogen (H₂) and ammonia, the thermally texturing comprisesdecomposing the light-transmission layer at the exposed portions intochemical constituents of the III-V semiconductor material andredepositing to form a plurality of crystals of the III-V semiconductormaterial having triangular crystal facets; and stopping the thermaltexturing by locally stopping the decomposing and redepositing at aninterface formed by the stop layer and the light-transmission layer,wherein the stop layer has a decomposition temperature that is higherthan that of the light-transmission layer such that texturing isprevented from extending into the stop layer.
 2. The method of claim 1,wherein the decomposing comprises heating to a temperature that issufficient to decompose the crystalline III-V material whileinsufficient to decompose the stop layer.
 3. The method of claim 2,wherein the thermally texturing comprises the decomposing and theredepositing simultaneously in a single process.
 4. The method of claim2, wherein the III-V semiconductor material is a nitride semiconductorand the thermally texturing comprises providing nitrogen atoms of thenitride semiconductor at least in part by the decomposing and theredepositing in the atmosphere comprising the molecular hydrogen (H₂)and ammonia.
 5. The method of claim 1, wherein the thermally texturingis carried out at atmospheric pressure and less than 1250° C.
 6. Themethod of claim 1, wherein the III-V semiconductor material is selectedfrom the group consisting of GaN, InGaN, AlGaN, AlInGaN and InN.
 7. Themethod of claim 6, wherein the III-V semiconductor material is GaN, andthe stop layer is formed of AlN or AlGaN.
 8. The method of claim 6,wherein the III-V semiconductor material is InGaN, and the stop layer isformed of one of AlN, AlGaN or GaN.
 9. The method of claim 1, furthercomprising, after patterning the mask layer, removing at least portionsof the patterned mask layer and replacing with at least one metalcontact.
 10. The method of claim 1, wherein providing the light-emittinglayer stack comprises forming a light emitting element interposedbetween a p-type device layer and a n-type device layer by growing oneof the p-type device layer or the n-type device layer on a siliconsubstrate having (111) crystal orientation.
 11. A method of fabricatinga light-emitting semiconductor device, the method comprising: providinga light-emitting layer stack; forming a first nitride semiconductorlayer on the light-emitting layer stack and a polycrystalline secondnitride semiconductor layer on the first nitride semiconductor layer;patterning a mask layer on the second nitride semiconductor layer toexpose portions of the polycrystalline second nitride semiconductorlayer; and selectively texturing in an atmosphere comprising molecularhydrogen (H₂) and ammonia, the selectively texturing comprisesdecomposing the polycrystalline second nitride semiconductor layer atthe exposed portions into chemical constituents of the polycrystallinesecond nitride semiconductor layer and redepositing to form a texturedsecond nitride semiconductor layer comprising a plurality of crystals ofthe second nitride semiconductor having triangular crystal facets; andstopping the selective texturing by locally stopping the decomposing andthe redepositing at an interface formed by the stop layer and thepolycrystalline second nitride semiconductor layer, wherein theselectively texturing leaves the first nitride semiconductor layeruntextured.
 12. The method of claim 11, wherein the selectivelytexturing includes heating at a temperature that is sufficient todecompose the polycrystalline second nitride layer while beinginsufficient to decompose the first nitride layer, such that texturingis stopped from extending into the first layer.
 13. The method of claim12, wherein the selectively texturing includes heating at a temperaturebetween about 800° C. and about 1150° C.
 14. The method of claim 11,wherein the polycrystalline second nitride semiconductor layer is formedof a material selected from the group consisting of GaN, InGaN, AlGaN,AlInGaN and InN.
 15. The method of claim 14, wherein the textured secondnitride semiconductor layer is in a phase having a hexagonal crystalstructure such that the crystals have a pyramidal structure having thetriangular crystal facets.
 16. The method of claim 14, wherein providingthe light-emitting layer stack comprises providing a light-emittingquantum well stack prior to forming the first nitride semiconductorlayer thereon, wherein at least the polycrystalline second nitridesemiconductor is optically transmissive in light wavelengthscorresponding to an emission wavelength of the light-emittingquantum-well stack.
 17. The method of claim 16, wherein the selectivelytexturing includes heating at a temperature for a time durationsufficient to form the plurality of crystals having an average sizebetween about 300 nm and about 800 nm, such that a light transmissivityof the textured second nitride semiconductor is higher compared to alight transmissivity of the polycrystalline second nitridesemiconductor.
 18. The method of claim 16, further comprising doping thetextured second nitride semiconductor layer and the first nitridesemiconductor layer to form a p-doped region of the light emittingsemiconductor device, and wherein the active layer stack furthercomprises an n-doped region.